1. Field of Invention
The present invention relates to a speed changing mechanism and a speed changing control method thereof, and more particularly to a stepped automatic speed changing mechanism.
2. Description of Related Arts
Automatic transmission is an important component of the development and application of automobiles, which not only provides convenience for the driver, but also provides excellent comfort for the passenger. Furthermore, it can protect the power components of the vehicle, thereby prolonging the service life. The application of the automatic transmission can greatly simplify the driving operation, so the automatic transmission is the key component for the automobile commonly used.
After a hundred years of development, people invent the AT (hydraulic automatic transmission), and CVT (transmission ratio continuously variable transmission) and AMT (automatic mechanical transmission) in the automobile industry. In recent years, due to the influence of the energy problem, the hydraulic torque converter used by the AT has the low transmission efficiency, which seriously affects the development of AT. Therefore, CVT and AMT are developed instead of AT.
Due to the friction drive, the transfer torque and the durability of CVT are the biggest application barrier. Currently, CVT are mainly applied to the small displacement volume passenger vehicles. In spite that CVT are applied to the few high-grade large displacement volume vehicles, the market feeds back that CVT has a lot of problems, thereby some famous automobile manufacturers no longer continue to use CVT.
AMT has simple structure, low cost and high transmission efficiency, but it takes a long time to interrupt power transfer during the shifting process, thereby resulting in poor comfort. In order to solve the power interrupt problem, DCT (double clutch transmission), using two clutches to support the odd shifting and the even shifting, respectively, is invented. The shifting process is a process in which two clutches are switched, and has fast speed, thereby solving the inherent defects of AMT, and achieving the high-efficient transmission. However, DCT has complex structure and high cost. Simultaneously, it is difficult for DCT to control the friction clutch.
All transmissions mentioned above have the short-time power interruption during the shifting process except CVT for avoiding the transmission interference and protecting the shift conversion components. Therefore, it is desired for people to invent an automatic transmission with the high transmission efficiency, simple structure, low cost and capability of shifting without power interruption.